The present invention relates to a screw conveyor for transporting solid materials and including a feed screw formed, at least partially, as a shankless screw of a plurality of substantially band-shaped screw threads extending along an imaginary helical line, a jacket surrounding the feed screw, and a brush cooperating with the inner surface of the jacket.
Screw conveyors of the above mentioned type are well known. These conveyors serve for transporting or conveying of dry, wet, moisturized, pasteurized, sticking, dusty, and/or coarse solid materials. The Jacket envelops the feed screw to a greater or lesser degree. It is also possible to completely surround the feed screw to avoid problems associated with transportation of dusty, spreading and odorous materials. The screw and the jacket can be formed of metal, but also of plastic materials. The length of such screw conveyors can reach 40m, with the diameter being in a range of 20-2000 mm. The central axis of the feed screw can be inclined to a horizontal at an angle of from 0.degree. to 35.degree.. It has been established in many cases that the amount of the transported solid material very much depends on the inclination angle of the feed screw. In particularly, at an inclination angle of more than 35.degree., the materials fall through the free space of the shankless screw, and the delivery output of a screw conveyor can be reduced to zero.
International application WO/90/5100 discloses a screw conveyor having a shankless screw formed of at least two substantially band-shaped screw threads extending along an imaginary helical line. A particular type of a screw conveyor is designed for discharging solid materials contained in a solid-liquid mixture, which flows through a trough. Here the trough is, a transporting section for transporting solid-liquid mixtures. The known trough can be manufactured from, e.g., cement, steel, stainless steel, aluminum, plastics and other suitable materials. In addition, the screw conveyor can be mounted on a container for a solid-liquid mixture. The container maybe a receiving tank, an intermediate container, a storage container and the like formed of a suitable material. The jacket or sheath of a such screw conveyor is designed so that it can be penetrated by the flowing fluid and is formed as a sieve jacket extending into the trough at an angle.
The screw conveyor of this type comprises a closed tube in which the solid material is compressed, rinsed, if needed, and finally discharged into a collecting tank. For improving the flow characteristics of the feed screws, they, at least, in the region of the trough, are formed as a shankless screw, that is the central region of the screw is empty. This leads to that, at an inclination angle of the sieve jacket or the feed screw of more than 35.degree., the transported solid materials falls through the screw empty or free region and are not discharged. This leads to that, at different delivery heights, feed screws should have different length, and that substantially increases manufacturing costs.
Accordingly, an object of the invention is a screw conveyor devoid of the above-mentioned drawback and, in particular, a conveyor which can be used at a more steep installation angle than the conventional screw conveyors.